Sichuan Pepper's Buzz May Reveal Secrets Of The Nervous System

It's the Sichuan peppercorn in dishes like spicy ma po tofu that makes your mouth buzz. Researchers wanted to know if that buzz is connected to the tingling you feel when your foot falls asleep.

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Originally published on April 17, 2014 7:19 am

The Sichuan peppercorn is known to give some Chinese dishes a pleasant tingling feeling.

What's not so pleasant is that pins-and-needles feeling we get when our foot falls asleep — or when people who suffer from paresthesia experience constant tingling in their limbs.

Diana Bautista, a neuroscientist at the University of California, Berkeley, wondered: Could these sensations be connected?

Bautista says a lot of what we know comes from studying plants that give us unique sensations — how we experience the heat of a chili pepper, for instance, or the coolness of a mint leaf. So when Bautista decided to investigate what goes on inside nerve cells when we get a tingling, numbing sensation, she turned to the berries of the prickly ash tree — known in Chinese cooking as the Sichuan (also sometimes spelled "Szechwan") peppercorn.

When I visited her lab, Bautista had told me what to expect while tasting the pepper: "You get sort of a wave of different sensations. First, I experienced a light citrus flavor ... and then you start to a little bit of a prickling sensation ... and then when you think that it's ending, it's actually just about to start."

What Bautista wanted to know was: Why do we feel this mouth buzz from eating a bowl of spicy ma po tofu? Is the Sichuan pepper activating the same nerve cells that respond when your cellphone buzzes or you use an electric toothbrush?

It's a tricky question, because there are 30 different kinds of nerve cells called somatosensory neurons, and they each respond to different tactile sensations.

Bautista recently made an important connection: When she exposed a bunch of mouse neurons for touch, itch and pain to shanshool, the ingredient that gives the pepper its buzz, only the big ones responsible for touch and vibration reacted.

"So we were really excited, and it is the first compound that specifically targets the touch pathway," she says.

But that's not all. The Sichuan pepper not only chemically mimics touch, but also activates "the same neurons that are affected in patients who suffer from tingling and numbing paresthesia," she says.

Her discovery may help lead to finding ways to switch off the buzzing feeling for people who live with this tingling sensation all the time.

Researchers are using Bautista's finding in other ways, too. Nobuhiro Hagura, a neuroscientist at University College London, wanted to know whether everyone experiences those peppery vibrations in the same way — in the way we all hear the same note in music. He wrote a paper called "Food Vibrations" for the British journal Proceedings of the Royal Academy.

"The bottom line is very simple: We wanted to know what is the frequency perceived by Sichuan pepper, and is it consistent across participants?" he says.

Hagura designed a neat experiment. Twenty-eight willing volunteers came to his lab, and instead of giving them some spicy takeout, they each got enough sanshool extract to make their mouths tingle. Each of them also got a small box that could vibrate a bit like a cellphone.

The task for the tingling volunteers was to try to match the peppery vibrations in their mouths to the vibrations they could feel in their fingertips as the researchers dialed the frequency of the box up or down — "They are closing their eyes and they're saying 'higher' or 'lower,' so it's kind of a bizarre situation," says Hagura — until the Sichuan buzz and the mechanical buzz converged on the same frequency, which turns out to be 50 hertz.

Scientists are still looking for other plants that could help unlock the secrets of our sensory nerves. And that ingredient just might be hiding in your pantry.

Copyright 2014 NPR. To see more, visit http://www.npr.org/.

Transcript

DAVID GREENE, HOST:

You probably know the feeling of pins and needles; a numbing, tingling sensation that can be pretty unpleasant but probably short lived. Unless you happen to be one of the millions of Americans who suffer from something known as tingling and numbing paresthesia. It's a chronic and fairly common condition in which the uncomfortable prickling feeling doesn't go away, and even becomes debilitating. Researchers do not fully understand what causes this constant tingling or how best to treat it.

But as Ike Sriskandarajah reports, a possible key to the mystery lies in an unexpected place.

(SOUNDBITE OF CHOPPING)

IKE SRISKANDARAJAH, BYLINE: Mission Chinese in San Francisco is a restaurant, not a science lab. But I am here because of a science researcher. Diana Bautista is at the Department of Molecular and Cell Biology at UC, Berkeley and an expert on our sense of touch.

DIANA BAUTISTA: A lot of what we know has come from studying interesting plants that give us unique sensations.

SRISKANDARAJAH: How we experience the heat of a chili pepper, for instance, or the coolness of a mint leaf. So when Bautista decided to investigate what goes on inside nerve cells when we get a tingling, numbing sensation, she turned to the berries of the prickly ash tree; better known in Chinese cooking, as the Sichuan peppercorn. It's famous for the strong, vibrating buzz it makes in your mouth.

Jesse Koide, head chef at Mission Chinese brings a taste.

JESSE KOIDE: OK. So, I just wanted to bring these out. These are the three forms of Sichuan peppercorn ingredients that we use.

SABRINA RAMOS: Should I put multiple? The oil is going to be very scary - nervous.

SRISKANDARAJAH: When I visited her lab, Diana Bautista had told me what to expect.

BAUTISTA: You get sort of a wave of different sensations. First, I experienced a light citrus flavor.

SRISKANDARAJAH: It's very flowery.

BAUTISTA: And then you start to feel a little bit of a prickling sensation.

CHRIS EDLEY: It just hit the tip of my tongue like a burst.

SRISKANDARAJAH: And at its apparent apex...

BAUTISTA: And then when you think that it's ending, it's actually just about to start.

(LAUGHTER)

SRISKANDARAJAH: Wow.

STEVE BACKER: Oh, I feel the buzz.

EDLEY: Oh, yeah. Oh, now I'm really kicking in.

(LAUGHTER)

SRISKANDARAJAH: Now, what Bautista - who's a neuroscientist - wanted to know was: Why do we feel this mouth buzz from eating a bowl of spicy mouthful of tofu?

Is the Sichuan pepper activating the same nerve cells that respond, say, when your cell phone buzzes or you use an electric toothbrush? It's a tricky question because there are 30 different kinds of nerve cells called somatosensory neurons, and they each respond to different tactile sensations.

So how do you figure it out?

BAUTISTA: You can look into the microscope.

SRISKANDARAJAH: In her lab, I'm staring into a dish full of somatosensory neurons taken from a mouse.

BAUTISTA: It's a mixed population of cells that includes touch, itch and pain neurons - all 30 types together.

SRISKANDARAJAH: Bautista says one day she took a mixed bunch of cells like these and exposed them all to an extract called sanshool, the active ingredient that gives Sichuan pepper its buzz. That's how she made the discovery. Most of the cells did nothing. But one type did respond - the big ones.

BAUTISTA: So the big ones are the ones that are sensitive to light touch and vibration.

SRISKANDARAJAH: Sichuan pepper was activating the very same type of cells that let you feel your phone vibrating.

BAUTISTA: And so, we were really excited and it is the first compound that specifically targets the touch pathway.

SRISKANDARAJAH: But that's not all. Not only does Sichuan pepper chemically mimic touch...

BAUTISTA: It turns out that Sichuan pepper activate the same neurons that are affected in patients who suffer from tingling and numbing paresthesia.

SRISKANDARAJAH: Which was a real find; for one thing, it finally gives scientists a way to study in the lab all the chemical and electrical steps that lead to the brain getting the message when your foot falls asleep. Researchers can now take touch cells, get them buzzing using the pepper extract, and then start to figure out exactly what's going on at the molecular level; which might suggest ways of switching off the buzzing in patients who live with this tingling, numbing sensation all the time.

And researchers have been using Bautista's finding in other ways, too. I came across a paper in the British journal Proceedings of the Royal Academy, wonderfully titled "Food Vibrations."

(SOUNDBITE OF SONG, "GOOD VIBRATIONS")

BEACH BOYS: (Singing) Good, good, good, good vibrations...

SRISKANDARAJAH: It was written by Nobuhiro Hagura, a neuroscientist at University College London, who wanted to know whether everyone experiences those peppery vibrations in the same way, like we all hear the same note in music.

(SOUNDBITE OF SONG, "GOOD VIBRATIONS")

BOYS: (Singing) Do-do-do-do-do, do-do-do...

NOBUHIRO HAGURA: The bottom line is very simple: We wanted to know what is the frequency perceived by Sichuan pepper and is it consistent across participants.

SRISKANDARAJAH: He designed a neat experiment. Twenty-eight willing volunteers came to his lab. And instead of giving them some spicy Sichuan take out, they each got enough sanshool extract to make their mouths tingle. Each of them also got a small box that could vibrate a bit like a cell phone. You can sort of imagine the scene.

(SOUNDBITE OF SONG, "GOOD VIBRATIONS")

SRISKANDARAJAH: The task for the tingling volunteers was to try to match the peppery vibrations in their mouths to the vibrations they could feel in their finger tips, as the researchers dialed the frequency of the box up or down.

HAGURA: And they are closing their eyes and they're saying higher or lower, so it's kind of a bizarre situation.

SRISKANDARAJAH: Until the Sichuan buzz and the mechanical buzz converged on the same frequency, which turns out to be 50 Hertz.

(SOUNDBITE OF A 50 HERTZ TONE)

SRISKANDARAJAH: That's the sound of how the Sichuan pepper tastes.

Scientists are still looking for other plants that could help unlock the secrets of our sensory nerves. And who knows? Maybe there's a whole somatosensory symphony just waiting to be heard.